Saturday, February 15, 2014

Acetic Acid and Sodium Bicarbonate (AKA Vinegar and Baking Soda)

For our inaugural Saturday, we went with the old stand-by: Vinegar and Baking Soda. Really? The Bobby Brady volcano? Yup! That's the one.

First, the science.

Solid Baking Soda (Sodium bicarbonate: NaHCO3) and aqueous (or dissovled in water) Vinegar (Aceitc acid: CH3COOH) react to become liquid Water (H2O), gaseous Carbon dioxide (CO2) and Sodium acetate (C2H3NaO2). If you want to get all chemistry about it:

NaHCO3(s) + CH3COOH
(aq) àH2O(l) + CO­2(g)
+ C2H­3NaO2(aq)

The reactants, or ingredients, are commonly found in any kitchen. Vinegar is usually about 5% (by volume) Acetic acid. The other 95% is water. Sodium bicarbonate is a solid, which is not mixed with anything, traditionally (except in Baking Powder...don't use Baking Powder!).

The reaction is slightly exothermic, meaning that it releases a small amount of heat. The product, Carbon dioxide, is released as gas, and is seen as bubbles rising to the surface. The product, Sodium acetate, is soluble, meaning it dissolves in water.

There are a few pieces of evidence that a reaction can produce:

Color Change

Temperature Change

Bubbles

Appearance or disappearance of a solid (called a precipitate). This can sometimes be seen as cloudiness in the solution.

In this reaction, our primary evidence is the gas release, causing bubbles. The temperature change is slight and the Sodium acetate can't be seen because its dissolved.

Are you sweating yet? Don't worry. That's the end of the Chemistry lesson.

When I told the Science Kid that it was time to do an experiment, she ran upstairs to put on her Minnie Mouse dress and to grab a magic wand. Seems logically enough.

I asked her what she thought would happen when I mixed the two together. She held up her hands and said "I don't know!" And why should she? So we mixed 1/8 cup of vinegar and 1 teaspoon of baking soda (we'll get to the metric system later....don't worry!). Bubbles. "Whoa!"

Next, we kept with the same amount of vinegar, but measured out two teaspoons. BEFORE, she dumped it in, I made the SK predict what she thought would happen. "More Bubbles!" and again in another glass with three teaspoons.

We used the same type of glass each time, so we could see how far up the bubbles reached. We marked the highest spot with a dry erase marker. This way, we could compare after the reaction was finished.

SK made an observation that there was still 'white stuff' at the bottom of the glasses. How do we get rid of it? More vinegar! Now we abandoned measuring, and just had some fun.

Eventually, there stopped being so many bubbles. Why? SK once again threw up here hands "I don't know!". We looked at the bottom of the glass and noticed that the baking soda was almost gone. In science talk, the reactant was depleted.

We then turned our attention to one of the other glasses. Even though we left it alone, there were still bubbles emerging slowly from the baking soda at the bottom of the glass. When the vinegar was in low concentration, the reaction still took place, but very slowly.

First Science Saturday in the bag. Bath time! While we are splashing with bubbles, I get the question "What happens if we mix the baking soda with water?". Apparently SK is a better scientist than her dad, because SHE remembered that we needed a control group! SK made a prediction, we tried it out. Nothing. Because, as we discussed you need both reactants to make the reaction happen. SK waved her magic wand, and thus concluded our first Science Saturday!